"You're not very good at this, are you?"
Well, no. But then again, no one is very good at something they just started doing, are they? And add to that, if they think they are good, there's a high probability that they are in fact bad at it. But that's not what your inner voice wants to say, so instead you're stuck hearing about how you suck at this, and look at that person over there - they're good at this. Nevermind introducing logic to this conversation. Your inner voice doesn't care that the other person has years of experience. You get to hear yourself compared and found wanting.
And even if you do hear outside voices saying that you're doing well, you're catching on, that inner voice doesn't admit defeat and shut up. They're just being nice. They don't see the flaws, they are being patronizing. You should be learning faster. You can do better than this. You're lazy, worthless, should just toss it all and walk away.
The inner voice takes a lot of time and patience to tame and turn into a useful check instead of a full-on stumbling block. Some of us need a fair amount of outside support to get a handle on it. The first, and possibly the most important step, is to be aware that your inner voice is an unreliable narrator. In story telling, the unreliable narrator can be used to good effect, to lure the reader into a tale, and only reveal much later that what seemed solid and rational was all a lie. I'm reminded of the voice in the video game Portal, telling the player they are going to die, with a petulant tone. I always want to answer back: Look, 'bot, we're all going to die. That's true. But when? And where? That's not something you get to say, except inasmuch as you are trying to cause the player's death. The inner voice is like this, too. You're failing, it says. So you, programmed to obedience, do as you're told and fail. Told you so. The voice sits back in satisfaction. Now we can wallow in our misery.
So if you can't trust the inner voice, who can you trust? This is the tricky bit. You have to trust someone, and slowly that can be used to guide yourself into the ability to trust yourself. It's like training a puppy. Or a toddler. Don't lie about stuff Mama just watched you do. To bring the metaphor forward, if you were just hired - out of a mess of other applicants. Perhaps hundreds, and you, just you, made the final cut - they didn't see failure in you. They saw something the inner voice refuses to admit exists. A person that is valuable to them.
In more personal relationships the inner voice is insidious. If someone is wanting to be with you, and saying they care, your narrator is wondering what is wrong with them, that they can be so easily misled by your foolery. If you're alone, the Inner Voice is putting their nose in the air with a sniff and pointing out that you are utterly repellant, so why even try? It requires a very strong and determined person to worm their way past that, let me tell you, and that's the voice you ought to listen to. If they are treating you with love and caring, trust them when they tell you you're awesome. And when that doesn't work, listen to other friends who stand outside that inmost circle, and what are they saying?
Go for it. You can do this. You are stronger than you think you are.
I promise, you're going to be good at this. You just need some practice. C'mon, let's do it together.